The invention relates generally to a process and apparatus for hydraulically separating objects of differing specific gravities, and more particularly to hydraulic removal of stones from beans and other legumes.
In the preparation of dried beans for use in chili, tacos and other human foodstuffs, it is very important to remove all stones to avoid dental injuries. Stones commonly become mixed with beans during harvest. The beans are customarily "field-cleaned" after harvest using air separation and screening apparatus resembling that disclosed in U.S. Pat. No. 1,080,069 to Lyng. However, air cleaning only removes light materials and screening does not remove stones having sizes equal to or smaller than the size of the beans. On the average, a 100 pound sack of beans includes about 200 stones after screening. Consequently, further cleaning is required to remove the remaining stones before the beans can be prepared for consumption by humans.
It is known that vegetable matters and stones have differing specific gravities. Accordingly, apparatus for hydraulically separating or cleaning foodstuffs by specific gravity have been proposed in U.S. Pat. Nos. to Cleveland, 2,422,657; Olney, 2,945,589; Rakowsky, 2,879,889; Wallace, 3,792,772; and Peterson et al., 4,111,798. However, these devices do not reliably separate stones from beans. Both beans and stones have a specific gravity greater than water or brine, and the specific gravity of the stones is greater than, but often very close to that of beans. Existing hydraulic separation methods and apparatus are too innaccurate to separate objects of such close specific gravities with complete reliability.
Exposure to water during separation softens the dried beans, making it necessary to cook them promptly after separation. Consequently, separation must ordinarily be accomplished at the location where the beans are to be cooked. This presents no difficulty for large-scale commercial food processors, but effectively precludes small-scale users, such as restaurants, from using existing hydraulic separation devices. Existing devices generally tend to be rather complicated, bulky and expensive, rendering them unsuitable for small-scale users. Consequently, such users must either buy pre-cooked beans or separate stones from dried beans manually. However, the processed beans cost much more than dried beans and manually separating stones from beans is not only expensive because of the high labor cost involved, but also unreliable because the percentage of stones among the beans is small and the stones are easily overlooked.
Thus, restaurants and other small-scale users of dried beans and the like continue to need a compact, inexpensive and highly reliable means for removing stones on the premises immediately prior to preparing the beans for human consumption.
The concept of hydraulically separating objects of different specific gravities has also been applied more broadly, for example, in placer mining for gold. One example of such apparatus is disclosed in U.S. Pat. No. 1,151,722 to Schiechel. Schiechel teaches the use of an upward current of water to buoy lighter particles of sand upward to separate them from the heavier metallic particles, and pulsating the current to hydraulically agitate the particles to assist in their separation. However, this apparatus is more complicated than necessary, requiring pressurized sources of both water and air. In addition, feed stock is added at the top of the apparatus. This results in mixing of the feed stock into the upwardly flowing sand and water so that some of the heavier metallic particles are prevented from sinking, and, thus, are not reliably separated.